This invention relates to a water jet propulsion system for watercraft wherein pressure is applied by an impeller driven by a prime mover of the watercraft to water drawn through an opening at the rear portion of the bottom of the watercraft to eject jet streams of water rearwardly of the watercraft through fixed blades and a nozzle located downstream of the impeller, and more particularly it is concerned with improvements in or relating to a transmission for driving the impeller.
In this type of water jet propulsion system, the precision with which the impeller driven for rotation by a drive shaft of the prime mover for the watercraft is mounted on the drive shaft with respect to a duct surrounding the impeller for providing a path of flow of streams of water is a governing factor in increasing the efficiency with which propulsion of the watercraft is achieved by water jets. Thus it is imperative that positioning of the impeller be effected accurately. However, it is troublesome and time-consuming to carry out operation to obtain correct positioning, and particularly when the impeller is of the oblique flow type great difficulties are faced with.